1. Field of the Invention
The invention relates to an electron microscopy system for electron-microscopically obtaining information about a structure of an object. The invention further relates to a method for obtaining such information.
2. Brief Description of Related Art
Electron microscopes of the SEM type (scanning electron microscope) are known from the prior art.
In an electron microscope of the SEM type, a finely focused probe-forming primary electron beam is scanned across the object surface, and an integral secondary electron intensity is detected in dependence of a location of a beam spot formed by the finely focused primary electron beam in the object plane in order to obtain an electron-microscopic image of the object. In such an electron microscope, the achievable position resolution of the image is restricted substantially by a diameter of the beam spot of the primary electron beam in the plane of the object surface. The secondary electrons are detected integrally, i.e., position-independent. The detected secondary electron intensity is allocated to a location on the object to obtain a two-dimensionally position-resolving electron-microscopic image of the object. The position to which a detected secondary electron intensity is allocated in the image corresponds to the location on the object surface to which the primary electron beam is focused. The knowledge of this location and of changes of this location, respectively, is essential for the position resolution of the obtained image.
In the electron microscopy of the SEM-type there is usually provided a deflecting system in the beam path of the primary electrons in order to displace the primary electron beam away from an optical axis of an objective lens of the microscope. It is also possible to displace the sample relative to an objective lens of the electron microscope in a known or predetermined manner.
Since the secondary electron intensity is detected integrally and since the position information in the electron-microscopic image is obtained on account of the knowledge of the location of the primary electron beam spot in the object plane, the conventional electron microscope of the SEM type does not comprise a position-sensitive detector.
Applications of the electron microscope of the SEM-type are well known in the art. Two adjacent portions of the object differing in their efficiency to generate secondary electrons from incident primary electrons result in a contrast in the image, and the information which can be gained about an object by using the electron microscope of the SEM-type is limited to such structures which show differences in their secondary electron generation efficiencies.